1. Technical Field
This invention relates to hybrid vehicles having alternative power sources such as an electric motor and an internal combustion engine, and more particularly to energy management systems for such vehicles which efficiently uses the available power from such energy sources to drive the vehicle as well as operate subcomponents.
2. Discussion of the Prior Art
Hybrid vehicles generally consist of electric traction motors that drive the wheels, storage batteries for energizing the traction motors, and some type of generator driven by an internal combustion engine as an alternative means of energizing the traction motors. A regenerative braking system is desirable for a hybrid vehicle because it allows the traction motors to function as generators during braking and thereby electrically recover a portion of the vehicle's kinetic energy. During braking, the generators convert the vehicle's kinetic energy into electrical energy rather than dissipate such energy as waste heat as do conventional brakes. Under most operating conditions, this electrical energy is used to recharge the storage batteries. When the battery is at or near a fully charged condition, the regenerative braking system must be deactivated, and the recoverable kinetic energy must be dissipated by the conventional brakes. Whenever regenerative braking is turned off, either automatically (due to a fully recharged battery) or manually, the required brake pedal force and travel exerted by the driver to maintain a specific deceleration rate will be different depending on whether regenerative braking is on or off. This is commonly referred to as a change in brake pedal "feel". Such changes in brake pedal feel are generally considered unacceptable by the driver.